Thermionic device



Aug. 29, 1933. A w HULL AL 1,924,318

THBRMIONIC DEVICE Filed April 10, 1928 J Flg. 2.

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j\ v I g m 2a zz Invehtors: AlbertW. Hui], William A.Ruggles, y MW Their Attorneg.

Patented Aug. 29, 1933 UNITED STATES PATENT? OFFICE TBERMIONIC DEVICE Application April 10, 1928. Serial No. 268,976

13 Claims.

The present invention relates to electrical discharge devices and in particular to the cathode structure of such devices.

It is the object of our invention to provide thermionic cathodes for such devices which are long lived and have a greater thermal efficiency of electron emission than cathodes heretofore employed.

Our invention relates to multicellular thermionic cathodes which are constructed to provide a plurality of cavities open to the exterior and having an internal electron emitting surface area which is large relative to the external surface of the cathode. In our improved cathodes thermal losses are so greatly reduced that the energy required to maintain the cathodes at an operating temperature is only a small fraction of the energy required, for equal electronemitting area, with ordinary cathode structures such as are commonly employed in high vacuum tubes.

The novel features of our invention will be described in greater detail in the following specification taken in connection with the accompanying drawing.

' Referring to the drawing, Fig. 1 shows in perspective, and partly broken away, an electrical discharge device having three electrodes including a cathode embodying our invention; Fig. 2 is a vertical section on a larger scale of the cathode structure shown in Fig. 1; and Figs. 3, 4 and 5 illustrate in perspective modified forms of a cathode structure embodying our invention, the enclosing members of the cathode being shown partly broken away.

The device shown in Fig. 1 is illustrative of the type of devices to which our invention is applicable. It comprises a sealed envelope 2 into one end of which is sealed the leading-in wire 3 of the anode 4, the latter consisting of graphite, nickel, tungsten, or other suitable material. The wire 3 is connected to the usual external contact device 5. At the opposite end of the elongated envelope is provided a stem 6 upon which 45 is mounted the cathode structure 7 and a surrounding grid 8. The cathode and grid are of such size as to occupy a large fraction of the central space in the envelope 2. As the construetion and arrangement of the grid 8 forms no 50 part of our present invention, it need be said only in this connection that it consists of suitable sheet metal, such as nickel into which holes are punched as shown, and is supported by the wires 9, 10 which are connected to a band 11 surrounding the stem 6, the wire 10 being continued through the envelope wall to an external contact device 12.

The cathode '7 as shown in greater detail in Fig. 2 comprises an inner cylinder 13 which is provided with a lining 14 consisting of a refractory insulating material such as magnesia, alumina, or thoria. Upon this cylinder 13 consisting of nickel, or a suitable, alloy thereof, tungsten or molybdenum containing thorium oxide, are mounted the longitudinal walls or vanes 15 which extend radially from itsexternal surface and which in turn are surrounded by an outer cylinder 16, which reduces heat losses from the vanes. The vanes 15 which also may consist of nickel or iron, may be cut away for the m greater part of their length at their edges intermediate the ends so as to reduce the heat conduction from said vanes to the enclosing cylinder 16.

Within the cylinder 13 is a heater 17 consisting of suitable refractory material, for example, such as tungsten. One end of the heater 17 is connected by welding, riveting, or otherwise to the thickened end wall 18 of the cylinder 13. The enlarged and thickened end wall 18 prevents overheating and alloyage of the heater and the metal constituting the cylinder 13. The opposite end of the heater is connected by welding or other suitable method to a conductor 19. The external cylinder is attached by welding, or other suitable method, to the wires 20, 21. The conductors 19, 20, 21 are sealed through the glass stem 6, the conductor 19 and the conductors 20, 21 being connected respectively to external contact devices 22, 23 of the base 24 whereby electric current is supplied to the heater 17 to maintain the heater at a desired operating temperature.

The envelope 2 preferably is highly evacuated and the parts of the device are denuded of gas and then a fixed gas, such as argon at a pressure of the order of 50 microns (1/20 of a mm.) of mercury or a drop of mercury or other suitable vapor-yielding material is provided within the envelope. It is the ionization of this gas which reduces space charge and permits of the emission of electrons at moderate voltages from cavities in the emitting electrode.

Fig. 1 shows a shield 25 mounted on the stem 6. It'is a function of this shield to prevent heating the base part of the device to such a high temperature that an undesirably high vapor pressure of mercury exists in it during operation. Preferably during operation the pressure of the vapor should be of the order of about ten microns (1/100 of a m.m.) of mercury. When a permanent gas, such as argon, is used then the shield 25 may be omitted.

The interior surface of the cathode enclosure and in particular the walls or vanes 15 are coated with a material of high electron emissivity such as barium, caesium, cerium, or a mixture such as Mischmetal or the oxides of these metals. For example, these interior surfaces of a nickel cathode may be coated with barium carbonate, the cathode then being heated to a temperature of about 1300 0., thereby decomposing the barium carbonate and forming a material of high electron emissivity. When thoriated tungsten or molybdenum are used a thorium layer is formed by reduction of the oxide by the usual heating process.

Figs. 3, 4 and 5 illustrate different forms of {vanes suitable for devices embodying our invention. The vanes 26 of the device shown in Fig. 3 consist of single sheets of metal having their ends bent at an angle, these bent-over ends then being sealed to the interior cylinder 13 and the exterior cylinder 16 respectively. As illustrated, the edges of the vanes are indented leaving ears 29 of small section which are joined to the enclosing shell 16, thus affording rigidity with but a poor heat conductive path from the vanes 26 to the shell 16. The structure shown in Fig. 4 shows vanes 27 which have a generally triangular shape, the long bases of the triangle being aflixed upon the interior cylinder 13 and the apexes 29' of the triangle being joined to the cylinder 16 as shown. thus also limiting heat conductivity to a small area.

The structure shown in Fig, 5 comprises vanes 28 consisting of sheet metal bent back upon itself so as to have a V-shaped section, the apex of the V being joined to the central cylinder 13 and the bent-over ends being joined to the cylinder 16.

The exterior of the cylinder 16 preferably is polished thereby reducing the rate of heat dissipation to less than one half the rate of dissipation which is characteristic of cathodes having the exterior surface of a heated cylinder coated with active material.

Fig. 5 shows another feature of our invention whereby the heat energy of the cathode is conserved, namely the provision of one or more external cylinders 30, 31 surrounding the cathode and being spaced away therefrom, and from one another. These external cylinders, which are in poor heat conducting relation to one another, act as heat shields. By the use of two such shields, as shown, the energy required to heat the cathode may be reduced to about one fifth the amount which would be required without their presence.

As the amount of active electron-emitting material can be applied upon a relatively large surface within the described multicellular cathodes, the economy of electron emission per unit of cathode heating energy secured by the coaction of the various features of our invention is very high. A cathode can be maintained at an operating temperature by means of our invention by an expenditure of one per cent of the heat input required for cathodes now in use in pure electron discharge devices.

Broad claims to the hollow or cavity cathode construction disclosed herein appear in the copending application" of A. W. Hull, Serial No. 156,713, filed December 23, 1926. That application also contains claims relating to the combination of a cathode and heat shielding means.

The claims in the present application, therefore,

1,924.,ars

are limited to improvements over the invention described and claimed in the application referred to above.

-What we claim as new and desire to secure by- Letters Patent of the United States is:

1. An electrode comprising a cylinder, a heater therein, vanes mounted externally on said cylinder, a coating material having high electron emissivity on said vanes, and a heat-conserving enclosure surrounding said vanes and having an opening for the egress of electrons emitted by said material.

2.. A cathode structure adapted for use with an electrical discharge device comprising a cylinder, a heater therein, longitudinal vanes mounted upon the external surface of said cylinder and a second cylinder open at one end externally surrounding said vanes, and a thermionic coating material on said vanes.

3. A cathode structure adapted for use with an electrical discharge device comprising a metal cylinder, refractory electrical insulating material lining said cylinder, an electrical resistance heater within said cylinder longitudinal vanes mounted externally upon said cylinder, an external housing surrounding said vanes, and provided with openings to the exterior and a thermionic material on said vanes.

4. An electrical discharge device comprising a plurality of electrodes, an enclosing envelope, and 105 a gas therein at a pressure of the order of a fraction of a mm. of mercury, one of said electrodes being constituted of an open-ended enclosure, a plurality of longitudinal vanes within said enclosure constituting partitions, a thermionically active material on said partitions, a heater for heating said material to an electron-emitting temperature and a heat-conserving shield surrounding said enclosure only.

5. An electrical discharge device comprising a plurality of electrodes, an enclosing envelope, an attenuated gas therein, one of said electrodes being constituted of an open-ended elongated tubular enclosure having an externally polished surface, a second open-ended tubular enclosure contained therein, a plurality of longitudinal vanes between said enclosures, an electrical resistance heater within said second enclosure and a thermionic material coating the surface of the vanes between said enclosures. 1

6. An electrical discharge device comprising a plurality of electrodes, an enclosing envelope, and a gas therein at a pressure sufficiently high to neutralize space charge, the cathode in said device being constituted of a plurality of nested en- 1 closures, a plurality of longitudinal vanes between said enclosures, a thermionic material on the vanes located between said enclosures, heat shields surrounding said enclosures, a lining of refractory insulating material within said inner enclosure and an electric resistance heater contained within said inner enclosure.

7. A themionic cathode comprising a metal enclosure having an opening in communication with the exterior of said enclosure, a plurality of wall 1 members in said enclosure, a material of high electron emissivity coating the interior walls of said enclosure, means for heating said coated walls, and a plurality of spaced heat shields surrounding said enclosure, at least one of which is secured to the enclosure, said shields being in poor heat-conducting relation to said enclosure and to one another.

8. A themionic cathode comprising a metal enclosure with an opening, said enclosure containing a plurality of wall members, the internal surface of said enclosure including the surfaces of the wall members being large relative to the external surface of the enclosure, a material of high electron emissivity coating the walls of said enclosure, means for heating said coated walls to an electron-emitting temperature, and a plurality of spaced metal shells surrounding said enclosure.

9. A thermionic cathode comprising a metal enclosure having an opening in communication with the exterior of said enclosure, a plurality of wall members in said enclosure, the internal surface of said enclosure including the surfaces of the wall members being large relative to the external surface of the enclosure, a metal member surrounding said enclosure, said member being poor heatconducting relation to the interior portions of the cathode and having a polished surface, a material of high electron emissivity coating theinterior walls of said enclosure, and means for heating said walls to an electron-emitting temperature.

10. An electrical discharge device comprising a sealed container, an attenuated gas therein, electrodes therefor one of which comprises a heater, and includes metal vanes in good heat conducting relation to the heater, an outer enclosing shell in poor heat conducting relation to said vanes, said shell having an opening for the egress of electrons, a material of high electron emissivity coating said vanes, and a plurality of heat shields successively surrounding said shell for conserving the heat required to maintain said electrode at an operating temperature.

11. An electrical discharge device comprising an envelope an attenuated gas therein, and cooperating electrodes, one of which comprises a heater, and vanes in heat-receiving relation thereto, thermionic material on said vanes, an enclosure surrounding said vanes and provided with openings communicating with the exterior of the electrode, and a second enclosure spaced from and surrounding said first enclosure.

12. A thermionic cathode comprising a heater, and including metal vanes in good heat-conducting relation to the heater, an enclosing shell having an opening and being joined to said vanes at portions of small section relative to the section' of said vanes and a material of high electron emissivity coating said vanes.

13. An electrical discharge device comprising the combination of an envelope, electrodes therein including a cathode, a gas therein at a pressure sufficiently high to permit of substantial ionization, said cathode comprising'an enclosure with an opening for the egress of electrons, said enclosure containing members which present electron-emitting surfaces in addition to those of the enclosure, said opening being small in comparison to the internal area of the enclosure including that of the additional electron-emitting surfaces, a material of high electron-emissivity in said enclosure, means located in said envelope for heating said enclosure, a metal shell forming part of the cathode structure and surrounding the heated portions of the enclosure in spaced relation.

ALBERT W. HULL. WILLIAM A. RUGGLES. 

